1. Field of the Invention
The present invention relates to wireless portable devices and particularly to improvements in transmitting and receiving electromagnetic signals at multiple frequency bands.
2. Background of the Invention
Today's wireless devices, such as laptops and computers that connect wirelessly to the cellphone network or internet must use antennas to transmit and receive wireless energy to and from the device. Today's cellphones and laptops typically require multiple antennas, each antenna designed for resonance or desired performance at a particular frequency band (such as cellular band, say in the 850-950 MHz band, the Bluetooth/WiFi band, say in the 2400-2490 MHz band, and so on). Computer makers and cellphone makers have difficulty with the mechanical design of their equipment, and spend a great deal of engineering time, research, and cost in manufacture for the bill of materials for the feedlines and connections between transmitter circuits, transceiver circuits, or receiver circuits and the antennas that are mounted or housed in the wireless device casing. In some cases, antennas must be oriented in the flip up top of a lap top, placed behind or in the display screen, and tiny coaxial cables run through the case hinges, to the motherboard mounted below the keyboard. Similar problems exist with cellphones, and all devices generally must meet or exceed certain federal or wireless carrier-imposed requirements for radiation efficiency for a wide range of device orientations. It is envisioned that as wireless proliferates, cellphones and laptops will require more and more separate radio frequency bands in order to offer connectivity and competitive services. It is not inconceivable to eventually have wireless portable devices requiring 10 or more separate frequency bands, where the term “band” here means a particular wireless standard or service that is distinct from another. For example, standards such as IEEE 802.11a, 802.11b, 802.11g, 802.15a, 802.15.3.c, Cellular telephone (European, Asian, or US spectrum), Bluetooth, WiMax, PCS, all represent different bands, as they generally have different RF frequency band allocations assigned to them. In the future, RFID tags, vehicles, wireless post it notes, equipment, shipping containers, and even clothing may also suffer the issue of having to provide multiple antennas for different RF bands.
Today, there are many passive antennas solutions that have been published in the literature, such as, for example, the broadband planar antenna developed by Prof Chen at The University of Texas. Using Fractal programming (genetic algorithms), it is possible to do computer simulations that eventually create an antenna design that offers resonance for several different frequency bands. Such antennas generally are developed by using field solver programs, where the field solver is set to optimize an antenna structure for a particular antenna performance over a specified range of frequencies (for example, the field solver may be set to find an antenna structure that has a low return loss, S11, of less than −13 dB over the range of frequencies of 2.4-2.9 GHz and 5.1-5.8 GHz, in order to accommodate Bluetooth and WiFi 802.11a, 802.11b, and 802.11g). However, planar antennas, when designed by an optimization program or set of algorithms, without the use of active antenna tuning, may result in a larger antenna than what is feasible for a small package (e.g. a small handset).
Recently, there have been some technical advances in active antenna tuning, some of which have been pioneered by Paratek Microwave in Nashua, N.H. Using active lumped elements, such as tunable capacitors, it is possible to allow for the active tuning of an antenna within a cellphone handset. Using electrically tunable capacitors, Paratek has pioneered a way to allow for active tuning of one or more cellphone antennas, as discussed in U.S. Pat. No. 7,369,828.
In U.S. Pat. No. 7,369,828 by Shamsaifar (owned by Paratek Microwave), the device can tune two different cellphone antennas for use on one of several bands of interest, where each distinct and separate antenna (one for high band and one for low band) has an active element that may be tuned. As described in U.S. Pat. No. 7,369,829, a cellphone antenna is designed specifically for cellphone bands, since today's cellphones generally provide a small Bluetooth antenna, separate and apart from the cellular antenna. In U.S. Pat. No. 7,369,829, there is described a method of transmitting and receiving RF signals from multiple frequency bands utilizing an electronically tunable multiple band antenna, comprising the steps of: providing a high band antenna with at least one voltage tunable varactor associated therewith, the high band antenna providing a first input to a controller; providing a low band antenna with at least one voltage tunable varactor associated therewith, the low band antenna providing a second input to the controller; and inputting control data to the controller and controlling a first bias voltage for biasing the at least one voltage tunable varactor associated with the high band antenna and a second bias voltage for biasing the at least one voltage tunable varactor associated with the low band antenna. By using a controller, the invention enables an antenna to be tuned.
The controller of the method in U.S. Pat. No. 7,369,828 can use a DC voltage supply to provide the DC voltage needed to bias the voltage tunable varactors. The high band antenna of the method taught in U.S. Pat. No. 7,369,828 can further comprise: a substrate; a patch element on the substrate; at least one voltage tunable varactor associated with the patch element; a DC bias point on the patch element; an RF input on the patch element; a temperature sensor; and a ground plane on one side of the substrate.
The low band antenna of the method taught in U.S. Pat. No. 7,369,828 can further comprise: a substrate; a patch element on the substrate; at least one voltage tunable varactor associated with the patch element; a DC bias point on the patch element; an RF input on the patch element; a temperature sensor; and a ground plane on one side of the substrate.
In a more specific embodiment of a preferred method of U.S. Pat. No. 7,369,829, the multiple band antenna is a quad band antenna and covers the following frequency bands and standards which only involve cellular telephone (cellular and PCS): 824-894 MHz; 880-960 MHz; 1710-1880 MHz; 1850-1990 Hz; GSM850; EGSM; GSM1800; and PCS 1900.
Paratek uses BST as a tunable dielectric material that may be used in a tunable dielectric capacitor. Paratek Microwave, Inc. has developed and continues to develop tunable dielectric materials that may be utilized in embodiments of the antenna tuners and tunable filters, and the tuners are not necessary limited to using BST material. This family of tunable dielectric materials may be referred to as Parascan by the company.
The term “Parascan” as used herein is a trademarked term indicating a tunable dielectric material developed by Paratek Microwave, the assignee of U.S. Pat. Nos. 7,397,329 and 7,369,828, and the idea of tunable dielectric materials have been described in several patents. Barium strontium titanate (BaTiO3-SrTiO3), also referred to as BSTO, is used for its high dielectric constant (200-6,000) and large change in dielectric constant with applied voltage (25-75 percent with a field of 2 Volts/micron).
Tunable dielectric materials including barium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 to Sengupta, et al. entitled “Ceramic Ferroelectric Material”; U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-MgO”; U.S. Pat. No. 5,486,491 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-ZrO2”; U.S. Pat. No. 5,635,434 by Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-Magnesium Based Compound”; U.S. Pat. No. 5,830,591 by Sengupta, et al. entitled “Multilayered Ferroelectric Composite Waveguides”; U.S. Pat. No. 5,846,893 by Sengupta, et al. entitled “Thin Film Ferroelectric Composites and Method of Making”; U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled “Method of Making Thin Film Composites”; U.S. Pat. No. 5,693,429 by Sengupta, et al. entitled “Electronically Graded Multilayer Ferroelectric Composites”; U.S. Pat. No. 5,635,433 by Sengupta entitled “Ceramic Ferroelectric Composite Material BSTO-ZnO”; U.S. Pat. No. 6,074,971 by Chiu et al. entitled “Ceramic Ferroelectric Composite Materials with Enhanced Electronic Properties BSTO Mg Based Compound-Rare Earth Oxide”. These patents are incorporated herein by reference. The materials described in these patents, especially BSTO-MgO composites, show low dielectric loss and high tunability. Tunability is defined as the fractional change in the dielectric constant with applied voltage.
Using the idea of tunable capacitance, and following on the above listed prior art, Paratek Microwave has developed a technology called Adaptive Impedance Matching Models (AIMM) which it currently demonstrates on its website at worldwide web site paratek.com as able to adaptively tune antennas.
Agile Materials, a company founded in 1999 as a spinoff of University of California, Santa Barbara, has also developed tunable wireless components for multi-band systems. Agile has successfully commercialized its proprietary method to harness the unique properties of a thin-film ferroelectric capacitors, which may be tuned over at least an octave of frequency range. Agile employees produced U.S. Pat. No. 7,202,747, “Self Tuning Variable Impedence Circuit for Impedence Matching of Power amplifiers,”, as well a U.S. Pat. No. 7,012,483, “Tunable Bridge Circuit”, both of which use a BST tunable capacitive material to affect a resonance change in a tuneable circuit. All of the aforementioned is known from the public prior art of record.